Regulated power supplies are essential to any electronic system because they maintain a constant output voltage or current for changes in the input line voltage, output load, ambient temperature, or time. Switching, step down regulators are preferred over linear regulators in many instances, because of their greater power efficiency in converting a large input voltage into a significantly smaller output voltage, and because of their smaller size. These regulators, also referred to here as "buck" regulators, operate under closed loop control to alternately increase and decrease the current (at a frequency of several hundred kHz or higher) in an inductor of a low pass filter, to maintain a ripple-free, regulated, DC output voltage. Buck regulators are particularly desirable in portable, battery operated computing and communication devices such as high performance notebook computers which require small size as well as high power conversion efficiency in a voltage regulator. These devices may require a regulated output voltage of 1.6 Volts DC (to run the logic computing circuitry such as the core processor) from an input line voltage that can vary in the range of 5-21 Volts DC.
The inductor current in a buck regulator is controlled by operating a transistor which switches the inductor between a high voltage near one supply node (typically at a positive voltage) and a low voltage near another supply node (typically ground). Increasing this switching frequency allows the use of smaller size passive devices (inductors and capacitors) in the low pass filter, making the regulator fit more easily in the portable computing device, yet still achieve a ripple-free output voltage. However, increased switching frequency can reduce power conversion efficiency because a transistor is switching more often, and therefore dissipating more power, in the same interval of time. Reduced power conversion efficiency in a regulator is very undesirable, particularly in portable, battery operated devices.